The human erythrocyte membrane displays four well-defined structural transitions over the temperature range 45 degrees to 80 degrees Centigrade. These can be readily seen in a sensitive differential heat capacity calorimeter, scanning at 20 degrees per hour. Using calorimetry, along with other methods such as fluoresence, circular dichorism, EPR and thermal gel techniques, these transitions are being experimentally characterized. Variables include pH, salt, divalent metal ions, proteolysis, anesthetics and drugs.